We plan to design antifolate agents guided by the properties of the target enzymes thymidylate synthetase and dihydrofolate reductase, the structure and activity of naturally occuring forms of folate coenzymes and the ability of folate analogs to inhibit microbial growth as well as the above mentioned enzymes. We will study the response of thymidylate synthetases isolated from L. casei, E. coli and coliphage T2 to polyglutamyl derivatives of folate and tetrahydrofolate. A P31 nuclear magnetic resonance study of the interaction of dUMP and thymidylate synthetase will be initiated. The aromatic amino acids tyrosine and tryptophan having their aromatic hydrogens replaced with deuterium will be incorporated into L. casei dihydrofolate reductase in order to assign the proton magnetic resonance peaks in the aromatic region of the protein spectrum. BIBLIOGRAPHIC REFERENCES: Leary, R.P., Beaudette, N. and Kisliuk, R.L., 1975, Interaction of Deoxyuridylate with Thymidylate Synthetase. J. Biol. Chem. 250, 4864-4868. Sharma, R.K. and Kisliuk, R.L., Verma, S.P. and Wallach, D.F.H., 1975, Study of Thymidylate Synthetase-Function by Laser Raman Spectroscopy, Biochem. Biophys. Acta, 391, 19-27.